// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_MEMORY_MEMORY_PRESSURE_MONITOR_CHROMEOS_H_
#define BASE_MEMORY_MEMORY_PRESSURE_MONITOR_CHROMEOS_H_

#include "base/base_export.h"
#include "base/files/scoped_file.h"
#include "base/macros.h"
#include "base/memory/memory_pressure_listener.h"
#include "base/memory/memory_pressure_monitor.h"
#include "base/memory/weak_ptr.h"
#include "base/timer/timer.h"

namespace base {
namespace chromeos {

    class TestMemoryPressureMonitor;

    ////////////////////////////////////////////////////////////////////////////////
    // MemoryPressureMonitor
    //
    // A class to handle the observation of our free memory. It notifies the
    // MemoryPressureListener of memory fill level changes, so that it can take
    // action to reduce memory resources accordingly.
    //
    class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
    public:
        using GetUsedMemoryInPercentCallback = int (*)();

        // There are two memory pressure events:
        // MODERATE - which will mainly release caches.
        // CRITICAL - which will discard tabs.
        // The |MemoryPressureThresholds| enum selects the strategy of firing these
        // events: A conservative strategy will keep as much content in memory as
        // possible (causing the system to swap to zram) and an aggressive strategy
        // will release memory earlier to avoid swapping.
        enum MemoryPressureThresholds {
            // Use the system default.
            THRESHOLD_DEFAULT = 0,
            // Try to keep as much content in memory as possible.
            THRESHOLD_CONSERVATIVE = 1,
            // Discard caches earlier, allowing to keep more tabs in memory.
            THRESHOLD_AGGRESSIVE_CACHE_DISCARD = 2,
            // Discard tabs earlier, allowing the system to get faster.
            THRESHOLD_AGGRESSIVE_TAB_DISCARD = 3,
            // Discard caches and tabs earlier to allow the system to be faster.
            THRESHOLD_AGGRESSIVE = 4
        };

        explicit MemoryPressureMonitor(MemoryPressureThresholds thresholds);
        ~MemoryPressureMonitor() override;

        // Redo the memory pressure calculation soon and call again if a critical
        // memory pressure prevails. Note that this call will trigger an asynchronous
        // action which gives the system time to release memory back into the pool.
        void ScheduleEarlyCheck();

        // Get the current memory pressure level.
        MemoryPressureListener::MemoryPressureLevel GetCurrentPressureLevel() const
            override;

        // Returns a type-casted version of the current memory pressure monitor. A
        // simple wrapper to base::MemoryPressureMonitor::Get.
        static MemoryPressureMonitor* Get();

    private:
        friend TestMemoryPressureMonitor;
        // Starts observing the memory fill level.
        // Calls to StartObserving should always be matched with calls to
        // StopObserving.
        void StartObserving();

        // Stop observing the memory fill level.
        // May be safely called if StartObserving has not been called.
        void StopObserving();

        // The function which gets periodically called to check any changes in the
        // memory pressure. It will report pressure changes as well as continuous
        // critical pressure levels.
        void CheckMemoryPressure();

        // The function periodically checks the memory pressure changes and records
        // the UMA histogram statistics for the current memory pressure level.
        void CheckMemoryPressureAndRecordStatistics();

        // Get the memory pressure in percent (virtual for testing).
        virtual int GetUsedMemoryInPercent();

        // The current memory pressure.
        base::MemoryPressureListener::MemoryPressureLevel
            current_memory_pressure_level_;

        // A periodic timer to check for resource pressure changes. This will get
        // replaced by a kernel triggered event system (see crbug.com/381196).
        base::RepeatingTimer timer_;

        // To slow down the amount of moderate pressure event calls, this counter
        // gets used to count the number of events since the last event occured.
        int moderate_pressure_repeat_count_;

        // The thresholds for moderate and critical pressure.
        const int moderate_pressure_threshold_percent_;
        const int critical_pressure_threshold_percent_;

        // File descriptor used to detect low memory condition.
        ScopedFD low_mem_file_;

        base::WeakPtrFactory<MemoryPressureMonitor> weak_ptr_factory_;

        DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitor);
    };

} // namespace chromeos
} // namespace base

#endif // BASE_MEMORY_MEMORY_PRESSURE_MONITOR_CHROMEOS_H_
